Diezel VH4 Pedal  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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The G
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Post by The G »

Most probably, the whine when using ICL7660 was caused by ICL7660 oscillating at audio frequencies (minimum 5kHz and typical 10kHz at 5V). Using the frequency boost pin on MAX1044 solves this problem by increasing the frequency about 6 times. ICL7660 doesn't have that pin, ICL7660S and MAX1044 have it.
A whine starting after a certain position of the gain potentiometer could be caused by positive feedback through the wiring or traces, and that is build specific. Have the gain pot at the whine start position and poke your wiring with a wooden stick, you might hear the whine react to certain wires moving. A buffer (or a buffered pedal) in front of the VH4 could also be of use.
Also, faster op amps oscillate easier.

On a side note, you could add a parallel resistor of around 56k to the 250k linear potentiometer to make it log, like on this page of R.G. Keen. The caveat is that the total pot resistance varies along with the pot position, but it doesn't seem to be a problem here.

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riffy
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Post by riffy »

yes. that boost pin really helped. no more audible whining. and what fixxed the problem was adding a pedal buffer at the input (boss DS-2 dual overdrive). now its dead silent even with gain/presense/treble/mid at max positions. I guess this circuit needs a low impedance source at its input.

boss pedals do have jfet(high imp input) & bjt(low imp output) as its 'bypassed' mode.


cheers!


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riffy
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Post by riffy »

ok. I was WRONG!

circuit schematic is fine, does NOT need buffer at its input. buffer(pedal) on input was just a bandaid solution, for the squeeling.

fix for whining? use the specified 7660S. OR use MAX1044 but max input is only 9v(still works fine && NO WHINE). I do have 7660S(ebay), can operate on 12v input but whines like HELL.

fix for SQUEELING? better board layout. I copied mine from edy_ (page4) and encountered squeeling with just 20% pot rotation. WAS fixxed by putting a pedal buffer up front.

after a ##few## sleepless nights, I thought i'd do star grounding.
basically all I did was gather each chip's GND points, and round em up on a common point, one where youd connect your power GND. and thats it. had to move some components so they dont share other GNDs..

NOW ITS SILENT. no more squeeling even at max settings. note that im just using B100K for the gain as at 50% rotation, there is nothing else more to 'gain' 😁

would love to redesign the board but naahhhhhh im lazy 😁 and its working FINE NOW.

btw freakin great pedal! big thanks to the guys for reverse engineering. this is my 3rd high gain pedal build. 1st was boss metalzone. 2nd was BE-OD(fixxed the squeel too, trimmer at MAX now). others are klon centaur and tightmetal(high gain?). maybe id do a last one, for the road (throttle box)

check out the before and after pics. :popcorn:

cheers!


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bmxguitarsbmx
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Post by bmxguitarsbmx »

For anyone that finds this pedal dark, I would recommend looking at the output resistive voltage divider. I found my build shockingly dark.

From Bajaman's schematic R36 = 150k and R37 = 100k. I changed to 47k/15k and kept C23 at 2n2. Cable capacitance can range from 75pF for a patch cable into a buffered delay pedal to 2nF for a low-quality 20 foot cable. Lowering this ratio may help keep the tone consistent. Your resistor ratio may vary, and you may wish to increase C23 in value to cut some top end which can be nice depending on your style. 150k/100k is a very large output impedance and will lose top end driving most anything. Initially, I removed C23, but that was not enough since it was driving a 1nF cable. Decreasing the ratio got me to a place where I re-installed the 2n2.

I also bypassed the 78L12 to get some more voltage on the rails. Cheers!

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DoomchildXXL
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Post by DoomchildXXL »

"shockingly dark" is a good way to put it. :)

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Post by avielnah »

need some assistance with this build, i build the PCB-Mania version, and while everything seems to work, the presence knob is not doing anything.
i checked the connections and values of the resistors/caps but they all look correct.
the depth knob, which is essentially coming from same opamp as the presence is working, so i am a bit clueless.
did you find your presence working as expected?

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bmxguitarsbmx
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Post by bmxguitarsbmx »

Check that you have the correct resistor value for R30. If you accidentally put a value that is too high, it will nullify the action of the presence pot.

Incidentally, the presence cap of 1uF is pretty big. It almost just acts as a volume control. I lowered that value to push its effect up into the presence region a bit more. Good luck!

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Post by avielnah »

bmxguitarsbmx wrote: 22 Jan 2022, 17:41 Check that you have the correct resistor value for R30. If you accidentally put a value that is too high, it will nullify the action of the presence pot.

Incidentally, the presence cap of 1uF is pretty big. It almost just acts as a volume control. I lowered that value to push its effect up into the presence region a bit more. Good luck!
well it works now, but as you said it is just doing volume, also the choice of C25K pot is strange, because to me only at about 8k i start hearing something going on. what value did you use for the cap?
i remember that in the youtube demos of the real pedal the presence knob is actually presence, and not volume

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bmxguitarsbmx
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Post by bmxguitarsbmx »

I used 220nF. I may try 100n, but 220n is much better. 1uF was useless to me.

I don't think a C10k would work for you. It might put the sweet spot of 8k lower than "1" on the dial. Where on the dial is your sweet spot right now? I deleted the 4k7 resistor that sets the gain at ~3. Deleting it drops it to near unity and makes the presence and resonance more active. I did other mods though so I don't know if that would get you what you wanted.

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Post by avielnah »

currently anywhere below 1 o'clock the presence is not doing anything, at the 1 oclock it starts reacting. i am wondering what more mods you did?

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Post by bmxguitarsbmx »

Thats probably good for a presence and resonance control. Amps act a lot like that. And, if you were to plug into the effects loop of an amp that has its own presence and resonance control, you might want them at zero with a fully flat response.

I did just swap mine to 100nF for the presence cap and I will keep it. Either is good. 100nF is the presence range. 220nF is still bumping mids imo.

I'll have to go through mine. I did a lot of piggybacking and didn't write anything down.

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Post by khstudio »

ERROR FOUND!

Hey guys, I don't get a chance to post much but really appreciate everyone and the time they take to invest and share.

Anyway... I purchased and built the Aion PCB and really love this pedal but I found it a hair dark and missing some air.
So I researched all the other schematics and pcbs available to see if there were any differences and they all appear to have the same discrepancy concerning the output connections.

It has been mentioned a few times about the output impedance being very high, which when working against the capacitance of 2n2 + any cable capacitance can drastically roll off signal, starting around 300 to 400 Hertz.
Now, I actually don't mind some of this roll off and was considering putting a potentiometer under the 2n2 output capacitor to ground, to give me a true presence control.
BUT... while scrutinizing the pictures that were shared, I think everyone (including Aion and the other PCB and kit suppliers) missed that the output voltage divider and capacitor to ground is actually connected to the "Out to Power Amp" Jack... NOT the "Out to Guitar Amp" Jack!!!

You can see this by looking at the pics, following the 150k Resistor Trace, which then goes to the jack "closest to the DC Power jack", which is the "Out to Power Amp".

It's not a game changer as all the pcbs available have both jacks but anyone like me that has already made and labeled a case, those connectors will be backwards.

Hopefully this is helpful!

But again I have to say that I like some of the Roll Off & Reduced volume of the "Out to Power Amp", just maybe not as much when plugging it directly into a guitar amp input... Fender Deluxe in my case.
When I use the wide open setting, that's supposed to go to "Out to Guitar Amp", it seems a little too open and too much!!
The "Out to Power Amp" has the 150k/100k divider w/ 2n2 to GND, which Knocks the volume down and rolls off... I actually prefer this going into my guitar amp input instead but like I said it's a "hair" too dark.

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Post by khstudio »

Ok... adding ^^ and updating my last post after testing and listening.... this is really puzzling!

So as I pointed out above, the voltage divider along with the capacitor to ground goes to the Power Amp Out jack... THIS output is definitely the best sounding and level to go into the front end input of the amp, NOT the effects return or power amp input (it's way too low signal for that)
Then the opposite is true, as the jack on the real Diezel pedal (Labeled for Amp Input) is wide open and very loud and bright without the voltage divider... This is way too hot and bright for the front end of a clean amplifier!!!

So did Diesel make a mistake labeling those outputs??

Please, I invite anyone to take a good look at the rear of the original pedal and Jacks, their labeling and position, then compare the pictures that were posted and linked to on the first page, then follow the traces back to the voltage divider and capacitor to ground... R36, R37, C23

This is really crazy!!
The good news is we can just use the opposite jacks and all should be well but definitely confusing When You're Expecting one thing and getting something else... and it all stems from the original pedal, from what I'm seeing.
Lmk and thx!!

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Post by khstudio »

Does anyone have this original pedal to confirm or check the outputs??

If so, a simple test to confirm exactly which output is:
A- louder and brighter
B- lower volume and darker

I know I'm late to this party but this is a great pedal... but it could be even better with a little tuning to the output filtering.
Also, if I am correct and it's labeled backwards on the original and drawn incorrectly on all the DIY projects, some may be using incorrectly or not getting the best results...
Especially when running the wide open louder signal (output) into the front end of an amp, which is way too hot and makes it want to feed back and oscillate!!
The lower darker output doesn't have any of those problems when running into the front end of an amp but is definitely a hair too dark, missing a little too much presence or air.

Anyway, just wanted to share my findings. Hopefully this is helpful or maybe helps improve an already killer pedal.

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Post by bmxguitarsbmx »

I have an original pedal. I immediately lent it out upon acquiring it. I'll have it back August 7th, if no one steps up till then. The original is very dark as well. I lent it to a buddy who owns an actual VH4. we'll see if he makes some clips.

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Post by khstudio »

bmxguitarsbmx wrote: 25 Jul 2022, 21:38 I have an original pedal. I immediately lent it out upon acquiring it. I'll have it back August 7th, if no one steps up till then. The original is very dark as well. I lent it to a buddy who owns an actual VH4. we'll see if he makes some clips.
Cool, Thx! Are you saying that the "Real VH4" pedal is "Just as DARK as the clone??" (I'm referring to the "Amp output" to front end of clean amp)

Anyway, I liked it so much I ordered one to compare to my build (AION PCB), But they sent me a Version 2 VH4-2 by mistake. It sounds and feels exactly like mine BUT it's more open in the hi end... mine sounds like a Presence control is stuck turned down. (And there are absolutely No Errors on my build!)

All PCB's available seem to have originated from this thread, using only pictures to reverse, so I wonder if something was missed by not having it "in hand"??

It's going to be harder to reverse my Ver-2 but I'm going to figure out what's up because the Real Pedal is KILLER!!!
Sadly, this won't tell me if there's a difference between V1 & the new V2 but I seriously doubt it's supposed to be that rolled off.

BTW, the 1st issues I posted about above is just puzzling... anyone can compare the pics in this thread to see what I'm talking about.

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Post by khstudio »

UPDATE, to my earlier ERROR Found post...

after further investigating, I think is possible the "voltage divider and capacitor to ground... R36, R37, C23" aren't going "to" the Power Amp Output, But coming "From" it.
It's not easy to trace using pics and I thought (and hoped) I'd found the cause of the Rolloff/Darkness

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Post by Saruman »

TLC1054 input 5...15V out 100mA F=40kHz

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Post by blackboarcult »

I did some simulations of this circuit in LTspice and I was actually quite puzzled at the behaviour of the zener diodes in the feedback loop of the 2nd gain stage.

All plots taken just after the gain stage w/5.6V zeners:
- In blue, no diodes.
- In red, D815A diode model.
- In turquoise, BZX384B diode model,
- In green, GP5V6 diode model.
Unfortunately the sims with 1N5232 were giving me a hard time and disproportionate gain amounts.

All diodes present a varying degree of low pass filtering. Earlier in the thread Baja talked about the input signal levels needed for those zeners to conduct being absurdly high and questioning their utility in the circuit, and also mentioned trying them in the third gain stage, getting "muffled"/dark results.

Sorry if it might seem obvious to anybody, but could the zeners be there simply for tone shaping and reducing the highs? or are my sims just misbehaving? :hmmm:
Does anybody have a knowledgeable explanation for this, or for their presence?
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Post by TBpedals »

Help!!!!!! I’m building a PCB Mania Benzin Vh4. I have signal passing however is quiet and has very little gain. Sounds more like a light overdrive. There is a lot of noise and whining specifically when I touch the gain pot with it maxed. I swapped out the pot for a spare I had laying around with the same issue. I have probed the signal and can confirm that it is passing IC1 correctly. It is losing signal strength somewhere before IC2. Any help is greatly appreciated.

https://pcbguitarmania.com/wp-content/u ... g-docs.pdf
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